This invention relates to an improved process for preparation of conjugated fatty acids from materials rich in fatty acids containing interrupted diene, triene and polyene systems. In a preferred embodiment the reaction produces approximately equal amounts of the conjugated linoleic acid isomers 9Z,11E-octadecadienoic acid and 10E,12Z-octadecadienoic acid from linoleic acid. The reaction is unique in that the reaction proceeds rapidly at temperatures as low as 90xc2x0 C. The process by-product stream is usable directly as a fertilizer that limits waste disposal costs.
Interrupted dienes moieties of fatty acids and esters thereof may be converted to conjugated dienes, and higher polymers may also be conjugated. For examples, literature reports the synthesis of conjugated forms of linoleic acid, linolenic acid and arachidonic acid using alkali catalysts. Of the conjugated fatty acids that have been prepared, conjugated forms of linoleic acid are the most investigated. Conjugated linoleic acid or CLA is the trivial name given to a series of eighteen carbon diene fatty acids with conjugated double bonds. Applications of, and uses for, conjugated linoleic acids vary from treatment of medical conditions such as anorexia (U.S. Pat. No. 5,430,066) and low immunity (U.S. Pat. No. 5,674,901) to applications in the field of dietetics, where CLA has been reported to reduce body fat (U.S. Pat. No. 5,554,646) and to inclusion in cosmetic formulae (U.S. Pat. No. 4,393,043).
Conjugated fatty acids, specifically CLA shows similar activity in veterinary applications. In addition, CLA has proven effective in reducing valgus and varus deformity in poultry (U.S. Pat. No. 5,760,083), and attenuating allergic responses (U.S. Pat. No. 5,585,400). CLA has also been reported to increase feed conversion efficiency in animals (U.S. Pat. No. 5,428,072). CLA-containing bait can reduce the fertility of scavenger bird species such as crows and magpies (U.S. Pat. No. 5,504,114).
Industrial applications for conjugated fatty acids also exist where they may be used as lubricant constituents (U.S. Pat. No. 4,376,711). Conjugation can be used as a means to chemically modify fatty acids, such as linoleic acid, so that they are readily reactive to Diels-Alder reagents (U.S. Pat. No. 5,053,534). In one method linoleic acid was separated from oleic acid by first conjugation then reaction with maleic anhydride followed by distillation (U.S. Pat. No. 5,194,640).
Conjugated fatty acids occur naturally in ruminant depot fats. The predominant form of conjugated fatty acid in ruminant fat is the 9Z,11E-octadecadienoic acid which is synthesized from linoleic acid in the rumen by micro-organisms like Butryvibrio fibrisolvens. The level of CLA found in ruminant fat is in part a function of dietary 9Z,12Z-octadecadienoic acid and the level of CLA in ruminant milk and depot fat may be increased marginally by feeding linoleic acid (U.S. Pat. No. 5,770,247).
Conjugated fatty acids may also be prepared by any of several analytical and preparative methods. Pariza and Ha pasteurized a mixture of butter oil and whey protein at 85xc2x0 C. for 5 minutes and noted elevated levels of CLA in the oil (U.S. Pat. No. 5,070,104). CLA produced by this mechanism is predominantly a mixture of 9Z,11E-octadecadienoic acid and 10E,12Z-octadecadienoic acid.
Conjugated fatty acids have also been produced by the reaction of soaps with strong alkali bases in molten soaps, alcohol, and ethylene glycol monomethyl ether (U.S. Pat. Nos. 2,389,260; 2,242,230 and 2,343,644). These reactions are inefficient, as they require the multiple steps of formation of the fatty acid followed by production of soap from the fatty acids, and subsequently increasing the temperature to isomerize the linoleic soap. The conjugated fatty acid product is generated by acidification with a strong acid (sulfuric or hydrochloric acid) and repeatedly washing the product with brine or CaCl2. Iwata et al. (U.S. Pat. No. 5,986,116) overcame the need for an intermediate step of preparation of fatty acids by reacting oils directly with alkali catalyst in a solvent of propylene glycol under low water or anhydrous conditions. Reaney et al., in U.S. patent application Ser. No. 09/451/710, entitled xe2x80x9cCommercial production of CLAxe2x80x9d, and Yurawecz, Mossaba, Kramer, Pariza and Nelson Eds. Advances in conjugated linoleic acid research, Vol. 1 pp.39-54 identified that conjugated fatty acid products prepared in the presence of glycol and other alcohols may transesterify with fatty esters and produce esters of the glycol. Such esters have been identified by Reaney et al. (unpublished data) in commercial products and in CLA prepared in propylene glycol by the method of U.S. Pat. No. 5,986,116. Esters of CLA containing fatty acids and propylene glycol have biological activity and therefore their presence in the CLA product is undesirable.
Conjugated fatty acids have been synthesized from fatty acids using SO2 in the presence of a sub-stoichiometric amount of soap forming base (U.S. Pat. No. 4,381,264). The reaction of linoleic acid with this catalyst produced predominantly the all trans configuration of CLA.
Efficient synthesis of 9Z,11E-octadecadienoic from ricinoleic acid has been achieved (Russian Patent 2,021,252). This synthesis, although efficient, uses expensive elimination reagents such as 1,8-diazobicyclo-(5,4,0)-undecene. For most applications the cost of the elimination reagent increases the production cost beyond the level at which commercial production of CLA is economically viable.
Of these methods, alkali isomerization of soaps is the least expensive process for bulk preparation of conjugated fatty acids. However, the use of either monohydric or polyhydric alcohols in alkali isomerization of conjugated fatty acids can be problematic. Lower alcohols are readily removed from the conjugated product but they require the production facility be built to support the use of flammable solvents. Higher molecular weight alcohols and polyhydric alcohols are considerably more difficult to remove from the product and residual levels of these alcohols (e.g. ethylene glycol) may not be acceptable in the conjugated product.
Water may be used in place of alcohols in the conjugation of fatty acids by alkali isomerization of soaps (U.S. Pat. Nos. 2,350,583 and 4,164,505). When water is used for this reaction it is necessary to perform the reaction in a pressure vessel whether in a batch (U.S. Pat. No. 2,350,583) or continuous mode of operation (U.S. Pat. No. 4,164,505). The process for synthesis of conjugated fatty acids from soaps dissolved in water still requires a complex series of reaction steps. Bradley and Richardson (Industrial and Engineering Chemistry February 1942 vol. 34 no.2 237-242) were able to produce conjugated fatty acids directly from soybean triglycerides by mixing sodium hydroxide, water and oil in a pressure vessel. Their method eliminated the need to synthesize fatty acids and then form soaps prior to the isomerization reaction. However, they reported that they were able to produce oil with up to 40 percent CLA. Quantitative conversion of the linoleic acid in soybean oil to CLA would have produced a fatty acid mixture with approximately 54 percent CLA.
Commercial conjugated linoleic acid often contains a mixture of positional isomers that may include 8E,10Z-octadecadienoic acid, 9Z,11E-octadecadienoic acid, 10E,12Z-octadecadienoic acid, and 11Z,13E-octadecadienoic acid (Christie, W. W., G. Dobson, and F. D. Gunstone, (1997) Isomers in commercial samples of conjugated linoleic acid. J. Am. Oil Chem. Soc. 74,11,1231).
The present invention describes a method of production of conjugated fatty acids using a polyether alcohol, such as polyethylene glycol alone or with a co-solvent as a reaction medium and vegetable oil, a fatty acid or ester thereof containing one or more interrupted diene moieties. In a preferred embodiment the reaction products of linoleic acid in polyether glycol containing solvent are primarily 9Z,11E-octadecadienoic acid and 10E,12Z-octadecadienoic acid in equal amounts. The reaction product is readily released by acidification.
In the present invention the quantitative production of conjugated fatty acids from fatty acids and esters containing interrupted dienes or higher polymers is achieved by heating the oil in a polyether alcohol with an alkali base. As it is normal for small amounts of water to be present in the reaction materials this water may either be boiled from the reaction mixture by addition of heat or reaction must be performed in a pressurized vessel; thereafter, the reaction mixture is neutralized by a strong acid, with solutions of H3PO4 being preferred. Surprisingly. when polyethylene glycol (PEG), and other polyether alcohols, are used as a solvent, the boiling reaction mixture does not foam uncontrollably. Surprisingly, the PEG solvent allows the reaction to proceed rapidly at temperatures as low as 90xc2x0 C. The selection of H3PO4 as the acid and KOH as the base allow the resultant salt solution to be disposed of in surface applications as a liquid or solid fertilizer. The reaction minimizes the production of undesirable isomers.
Thus, by one aspect of the invention there is provided a process for producing a preferred isomeric mix of a conjugated linoleic acid-rich fatty acid mixture comprising reacting a linoleic acid-rich oil with a base in the presence of a catalytic amount of said base, in a polyether alcohol solvent containing medium, at a temperature above 90xc2x0 C., and separating said conjugated linoleic acid-rich fatty acid mixture from said solvent by the addition of acid. In a preferred embodiment, 300 MW polyethylene glycol is the preferred polyether alcohol.